Patent Application
20110067377
The invention relates generally to methods for controlling the operation of gas turbine engines and, more particularly, to a method of controlling combustion dynamics in gas turbines.
Gas turbine engines include a compressor, a combustor, and a turbine coupled to the compressor. The combustor can include a plurality of combustor cans. Compressed air and fuel are delivered to the combustor cans to produce high-velocity and high-pressure combustion gases. These combustion gases are discharged to the turbine. The turbine extracts energy from the combustion gases for producing power that can be used in several ways such as, for example, to power the compressor, to power an electrical generator, or to power an aircraft.
Gas turbine engines operate under different load conditions that necessitate varying combustion operating conditions for the combustors to meet desired performance. Under some conditions, combustion phenomenon can interact with natural modes of combustors, establishing a feedback cycle. This leads to high-amplitude pressure fluctuations or perturbations. These pressure perturbations are referred to as combustion dynamics. Combustion dynamics are capable of restricting the operating conditions of the gas turbine and can also cause hardware damage or unscheduled shutdown.
Combustion dynamics is an issue faced by all types of combustors. Due to the design, combustion dynamics are relatively more severe for modern pre-mixed combustion systems that were developed in order to achieve reduced emissions. It would therefore be desirable to control combustion dynamics in gas turbine engines.
In accordance with one embodiment disclosed herein, a system comprises a gas turbine combustor having a plurality of combustor cans, crossfire tubes connecting the combustor cans, and a tubular connection system connecting the combustor cans to control combustion dynamics. The tubular connection system comprises tubes for connecting at least a pair of the combustor cans.
In accordance with another embodiment disclosed herein, a system comprises a gas turbine combustor having a plurality of combustor cans, crossfire tubes connecting the combustor cans, and a tubular connection system acoustically connecting the combustor cans to control combustion dynamics. The tubular connection system comprises tubes for connecting head-ends of at least a pair of adjacent combustor cans.
In accordance with another embodiment disclosed herein, a system comprises a gas turbine combustion system having a plurality of combustor cans, crossfire tubes connecting the combustor cans, and a tubular connection system connecting the combustor cans to control combustion dynamics. The tubular connection system comprises tubes for acoustically connecting combustor cans such that an acoustic wave resulting from combustion dynamics of a first combustor can reaches a second combustor can out-of-phase to reduce or cancel combustion dynamics in the second combustor can.
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
Embodiments disclosed herein include a system for controlling combustion dynamics in multi-can gas turbine engines. The system includes a dedicated tubular connection system connecting the combustor cans to control combustion dynamics. Although the system and method are described herein in the context of a heavy duty gas turbine engine employed for industrial application, the system and method are applicable to other combustion engine systems utilized in various applications such as, but not limited to, aircraft, marine, helicopter, and prime-mover applications. As used herein, singular forms such as “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.
Referring to
Surrounding the combustor liner is an annular shroud or casing 30 that defines an annular manifold around the liner through which the compressed air 24 is channeled in a conventional manner for both cooling the liner itself, as well as providing air to the pre-mixers.
The combustor 14 is annular and is generally symmetrical about a longitudinal or axial centerline axis of the engine, and includes a row of substantially identical combustor cans 16 as illustrated in
Combustion dynamics in can-annular combustion systems show acoustic pressure distributions that can be categorized into two modes. One mode is characterized by in-phase oscillations of adjacent combustor cans. In another mode, adjacent combustor cans fluctuate out-of-phase, i.e. the mode-shapes in two adjacent cans are out-of-phase. Due to the structure of the mode shape across the flow-path through the can, the pressure inside the head-end volume of a can also fluctuates out-of-phase compared to neighboring cans. Multi-can combustors also have a tendency to crosstalk between combustor cans via flow paths connecting those cans.
The tubular connection system 56 controls and eliminates combustion dynamics modes. In the embodiment shown in
The tubes 60 act as acoustic pathways. The larger flow area of the tubes 60 compared to can-to-can crosstalk 64 areas and the crossfire tubes 54 between the combustor cans 58 forces an additional pressure-node between the combustor cans 58. Because of the smooth pressure distribution that is enabled by the large flow area of tubes 60, the pressure amplitude inside the head-end 62 volume will be efficiently decreased.
If the diameter of the tubes 62 is appropriately large, there is no additional impedance step inserted and the smooth pressure distribution will force lower pressure amplitude inside the head-end volume and hence deforms the total mode-shape and shifts the frequencies of combustion dynamics. This will detune flame-heat-release excitation and combustion system acoustics and lowers the pressure amplitudes at the flame location and at the location of fuel injection and, therefore, damps the interaction between source, i.e. heat-release fluctuations of the flame, and acoustics.
Depending on circumferential mode-shapes that may be developed around the annulus, head ends of combustor cans 58 are connected in groups to disconnect the full annulus and cut the annulus into two or more parts. For example, in one embodiment 70 as shown in
In another embodiment 80 as shown in
As described previously, the combustor cans 104 are already connected through crossfire tubes 108 and crosstalk 110. Although a particular can is operating normally, combustion dynamics of other cans can drive normally operating combustor can through crosstalk or crossfire tubes. The criterion for various configurations of the tubular connection system is that an acoustic wave 112 resulting from combustion dynamics of a particular combustor can, reaches a connected combustor can out-of-phase with combustion dynamics in the connected combustor can, to reduce or cancel combustion dynamics in the connected combustor can.
For example, if combustion dynamics in first combustor can (Can ‘1’) is ‘+x’ units and combustion dynamics of the second combustor can (Can ‘2’) is out-of-phase at ‘−x’ units, then the acoustic wave 112 resulting from combustion dynamics of the first combustor can reaches the second combustor can and cancels the combustion dynamics of the second combustor can or vice versa. The higher the amplitude of combustion dynamics in one can, the stronger the cancellation force in the connected cans. For example, if the amplitude of combustion dynamics in first combustor can is ‘+2x’ units and the amplitudes of combustion dynamics of the second and fourth (Can ‘4’) combustor cans are each at ‘−x’ units, then the acoustic wave resulting from the first combustor can reaches the second and fourth combustor cans and cancels the combustion dynamics of the second and fourth combustor cans. The tubular connection system 114 therefore enables self-cancellation of combustion dynamics across connected cans 104.
In another embodiment as shown in
By tuning the length and choice of the cans the connections can be optimized for various modes/tones. For both in-phase and out-of-phase modes neighboring can connections as well as connections to non-adjacent cans may be considered. The length and size of tubes depend on the targeted frequency and its associated mode-shape. Further, the choice of connecting cans depends on the resulting tube geometry and available space between various cans. This may also necessitates direct connections to cans further away from the original can. In addition, the choice of connecting cans also depends on number of cans in the system that controls their separation.
The systems described above thus provide a way to control combustion dynamics in multi-can combustor systems by enabling acoustic interaction between the combustor cans. The system by itself limits, cancels, or controls combustion dynamics. The system can be used with existing gas turbine without any major modifications. The tubular connection system can be retrofitted to existing gas turbines. The design of the crossfire tubes connecting the combustion cans need not be changed.
It is to be understood that not necessarily all such objectives or advantages described above may be achieved in accordance with any particular embodiment. Thus, for example, those skilled in the art will recognize that the systems and techniques described herein may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objectives or advantages as may be taught or suggested herein.
While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.
